The invention relates to an improved process for the separation of unsaponifiable substances from crude sulphate soap, crude tall oil or tall oil pitch. Crude sulphate soap (CSS or BLSS) is a by-product of wood pulping and comprises sodium salts of fatty and rosin acids and an unsaponifiable neutral fraction which contains sterols and other neutral components, hereinafter called xe2x80x9cvaluable substancesxe2x80x9d or xe2x80x9cneutral substances.xe2x80x9d Crude tall oil (CTO) is made from this soap by acidulation, and tall oil pitch is the distillation residue of CTO.
The invention especially relates to the separation of the neutral substances by means of high vacuum distillation/evaporation, but it is also directed towards the production of fatty acids and other organic acids from the residues obtained from the high vacuum distillation/evaporation process.
Most processes used today to separate and concentrate neutral substances from either CSS, saponified CTO or saponified pitch use solvents, and these processes take advantage of the solubility differences between the unsaponifiable substances and the soap matrix. At present, when using one solvent alone, it is not possible to obtain a reasonable separation of the unsaponifiables from the fatty acid and rosin acid soaps etc. unless extreme process conditions, such as high temperatures and pressures, are used. Because of this, most processes often find it necessary to use more than one solvent, which complicates any recovery and reuse of the solvents, as well as tremendously increasing the costs of the processes.
Some processes for separating unsaponifiable neutral substances from CSS, saponified CTO, or saponified pitch use a high vacuum distillation/evaporation process. These processes take advantage of the volatility differences of volatile unsaponifiables, fatty acid, rosin acid, and almost any other non-volatile organic acid soap. In the case of separation by distillation, the difference between the boiling points of volatile products, such as unsaponifiable components, and the boiling point of different organic acid soaps is so remarkable that separation is possible at a high level of efficiency. However, a problem connected with this separation technique is the very high melting point required. This temperature is close to the decomposition temperature of sodium or potassium soaps (i.e. the sodium or potassium salts of fatty acids and rosin acids). It should be noted that even when melted, these soaps form extremely viscous liquids, which makes industrial handling difficult. While the soaps have to be kept at a high temperature (about 250xc2x0 C.) in order to maintain their flowability, they are irreversibly decomposed at this temperature, which compromises the separation output and the quality of the final product.
U.S. Pat. No. 3,887,537 discloses a process for recovering fatty acids and rosin acids from tall oil pitch by saponifying the tall oil pitch with an alkali metal hydroxide (sodium hydroxide) in the presence of an alkyl alcohol (such as butanol) to form soaps and unsaponifiables. This mixture is then fed into a thin film evaporator to evaporate and remove the low-boiling matter, including the light unsaponifiables, water and alcohol. Subsequently, the bottom fraction is fed into a second thin film evaporator for the purpose of removing unsaponified heavy material, including sterols. Finally, the bottom soap fraction obtained from the second evaporator is acidulated with a mineral acid to obtain the final product of fatty acids and rosin acids. It should be noted that one of the difficulties with this process is that the soaps are very viscous, thereby making the handling of the soaps troublesome.
WO 99/16785 discloses a method for separating unsaponifiable material from tall oil pitch by saponifying the pitch with a mixture of sodium hydroxide and potassium hydroxide to form sodium and potassium salts of fatty acids and rosin acids. The method then involves the evaporation of the unsaponifiable material which contains sterols using a thin film evaporator. The remaining unevaporated portion of the pitch which comprises sodium and potassium salts of the saponifiable material is then acidulated to create the rosin and fatty acids. Additionally, it is noted that this method also suffers from the previously discussed problem resulting from the difficulty in handling the sodium and/or potassium soaps.
WO 99/42471 discloses a method of separating sterols from tall oil pitch by saponifying the tall oil pitch with an alkali metal base comprising sodium hydroxide, potassium hydroxide or a mixture thereof, followed by neutralizing the saponified pitch with an acid and heating the neutralized pitch to remove water. The resulting pitch, which contains free sterols, is then evaporated to remove light ends. The remaining bottom fraction is then evaporated using a wiped evaporator to produce a light phase distillate containing free sterols. Subsequently, the light phase distillate is dissolved in a solvent comprising an alcohol, and the free sterols are crystallized from the solution by cooling. A disadvantage of this method is that the yield of the sterols is rather low.
U.S. Pat. No. 4,151,160 discloses a process for the separation of fatty acids from the unsaponfiable constituents contained in a head fraction of tall oil by converting the fatty acids into their zinc or lead soaps, and then removing the unsaponifiable constituents by vacuum distillation. Subsequently, the (remaining) non-volatile metal soaps are acidulated to produce the desired fatty acids. Typical components of the light boiling unsaponifiables are long chain alcohols and rosin degradation products, which have minor commercial value. It should be noted that the content of sterols in the tall oil heads is very low, considerably below 1% by weight, which shows that the tall oil head fraction is not a suitable source from which to produce sterols.
U.S. Pat. No. 4,483,791 discloses a process for the recovery of fatty acids from tall oil heads by converting the fatty acids contained in the tall oil heads into a mixture of magnesium soap and sodium soap, and then vacuum stripping the reaction product. Finally, the soaps are then acidulated to produce the desired fatty acids.
EP 0 952 208 A2 discloses a process for the separation of unsaponifiables from BLSS or CTO by dehydrating the raw material and melting and distilling the dehydrated material in a short path evaporation column. This publication also suggests adding unsaponifiables to the soap or neutralized crude tall oil before the drying step in order to reduce the necessary temperature required to maintain the mixture at a state of adequate fluidity during the drying process. The added unsaponifiables comprise recirculated unsaponifiables from the process and they are low boiling substances. The recirculated unsaponifiables have a favourable effect on the drying step but they are believed to have a disadvantageous effect on the subsequent distillation step as the low boiling unsaponifiables are evaporated with the sterol fraction, resulting in a dilution of the sterol fraction. Because they do not remain in the residue fraction, they cannot facilitate the handling of the residue with a viscosity reducing effect as would be the case if they were present in the residue.
The new process of the present invention has solved the problems associated with the already known evaporation processes for separating sterols and other valuable substances from crude sulphate soap, crude tall oil or tall oil pitch by incorporating a softener material into the saponified feed either prior to, after, or during the drying step, but prior to the evaporation step.
Thus, the present invention provides a process for separating unsaponifiable neutral substances from crude sulphate soap, crude tall oil or tall oil pitch, comprising the steps of:
(a) providing a feed of at least one of crude sulphate soap, saponified crude tall oil or saponified tall oil pitch,
(b) providing a softener and incorporating said softener into said feed to produce a mixed feed, wherein said softener possesses the following properties at the operation conditions of the process:
(i) the viscosity of the mixed feed having the softener incorporated therein is lower than the viscosity of the feed without the softener;
(ii) the vapour pressure of the softener is lower than the vapour pressure of the unsaponifiables of the feed;
iii) the molecular weight of the softener is at least 750; and, optionally,
iv) the softener is substantially immune to degradation and other side reactions caused by heat;
(c) drying said mixed feed to produce a dried mixed feed; and
(d) subjecting the dried mixed feed to a first high vacuum evaporation to obtain a product rich in unsaponifiable valuable substances in the form of a distillate.
Additionally, the present invention provides a process for separating unsaponifiable neutral substances from crude sulphate soap, crude tall oil, or tall oil pitch comprising the steps of:
(a) providing a feed of at least one of crude sulphate soap, saponified crude tall oil or saponified tall oil pitch,
(b) drying the feed of step (a) to produce a dried feed; and
(c) subjecting the dried feed to a first high vacuum evaporation to obtain a product rich in unsaponifiable valuable substances in the form of a distillate,
wherein a softener has been incorporated into said dried feed at any point prior to step (c), to produce a mixed feed,
wherein said softener possesses the following properties at the operation conditions of the process:
i) the viscosity of the mixed feed having the softener incorporated therein is lower than the viscosity of the feed without the softener;
ii) the vapour pressure of the softener is lower than the vapour pressure of the unsaponifiables of the feed;
iii) the molecular weight of the softener is at least 750; and, optionally,
iv) the softener is substantially immune to degradation and other side reactions caused by heat.
As stated above, the present invention has solved the problems associated with the already known evaporation processes for separating sterols and other valuable substances from crude sulphate soap, crude tall oil or tall oil pitch by incorporating a softener material into the saponified feed either prior to, after, or during the drying step, but prior to the evaporation step. Additionally, it has been found that it is preferred that the unsaponifiables of the feed be soluble in the softener; and that the residue remaining after the evaporation steps is also soluble in the softener. Most preferably, though, both the unsaponifiables and the residue remaining after the evaporation steps should be soluble in the softener.
It has also been discovered that the partial vapour pressure of the softener is preferably less than 10% of the partial vapour pressure of the unsaponifiable fraction at the evaporation conditions. It is also preferred that the softener is added to the feed in an amount of 1-500 wt-%, preferably 5-200 wt-%, and more preferably between 10 wt-% and 100 wt-%, calculated on the dry weight of the feed. Preferably, the viscosity of the mixture of feed and softener does not at any stage of the process (providing, incorporating, drying and evaporation) exceed 1.5xc3x97106 cSt (preferably it does not exceed 1xc3x97105 cSt). The distillation bottoms preferably also have a viscosity of at most 1.5xc3x97106 cSt.
It is also possible to use the above process without introducing a softener in the pre-drying stage. It has been discovered that the process retains its efficacy if the softener is added when the feed has already begun drying or is even when the feed is already dry. Preferably, though, the softener is added prior to the vacuum evaporation step.
The role of the softener material is to decrease the viscosity of the material, thereby preventing the inadvertent intake of matter into the equipment and, on the other hand, facilitating the removal of the valuable substances from the low viscous liquid bulk material in the evaporation unit. Not only should the softener have the above properties, but it is optionally substantially heat resistant, and thereby substantially immune to degradation (e.g. less than 10% by weight) and other side reactions occurring because of the conditions, such as elevated temperatures, employed in the process. However, if the softener does not possess these optional properties, then the conditions of the reactions should be regulated so that a sufficient amount of non-degraded softener will survive in order to obtain the intended effect.
Any compound which fulfils the above requirements can be used as softener in the claimed invention. Preferably, that the molecular weight of the softener should be at least 750 and no greater than 6,000. Examples of especially suitable softeners having a molecular weight of at least 1000, preferably at least 2000, are high boiling hydrocarbons; e.g. paraffin waxes, high boiling naphtenes, polyglycols, e.g. polypropylene glycol and polyethylene glycol, as well as high molecular weight silicon oils.
Also, high molecular weight esters defined as having an average molecular weight of about 800, e.g. triglyceride, can be used, provided that the process is operated in such a manner that a sufficient amount of softener remains in the residue following the evaporation step(s). This can be ensured by lowering the pH value of the process to a level of 7 to 10, preferably 8 to 9.5, so as to prevent or minimize the alkaline hydrolysis of the ester.
Preferably, the unsaponifiable neutral substances separated by the process of the present invention comprise sterols.
The feed of step (a) can be obtained by incorporating the softener into a feed of crude sulphate soap. Additionally, the feed of step (a) can also be obtained by saponifying a feed of crude tall oil or tall oil pitch, and subsequently incorporating the softener into the feed of saponified crude tall oil or saponified tall oil pitch. A third method by which the feed of step (a) can be obtained is by incorporating the softener into a feed of crude tall oil or tall oil pitch, and subsequently saponifying the feed having the softener incorporated therein.
According to a preferred embodiment of the present invention, the product which is rich in unsaponifiable valuable substances is obtained as the distillate from the first high vacuum evaporation. This distillate is then preferably subjected to a second high vacuum evaporation to remove light ends of said distillate, and to obtain a product enriched in unsaponifiable valuable substances.
This second product, which is enriched in unsaponifiable valuable substances, can then be subjected to a third high vacuum evaporation to obtain a product even further enriched in unsaponifiable neutral substances. Finally, it is possible to continue to subject the product of the evaporation steps to additional evaporation steps in order to further increase the concentration and/or purity of the neutral substances. Additionally, it is possible to combine all of the evaporation steps into a single process, thereby improving the efficiency of the overall process.
The high vacuum evaporation(s) is (are) preferably carried out in a short path evaporator or wipe film evaporator at a temperature in the range of 100xc2x0 C. to 350xc2x0 C. and at a pressure in the range of 25 mbar to about 1xc3x9710xe2x88x923 mbar or less. Also, the drying step is preferably carried out in a short path evaporator or in a wipe film evaporator.
According to the invention, the product rich in unsaponifiable valuable substances obtained from the first high vacuum evaporator or the product enriched in unsaponifiable valuable substances obtained from the second high vacuum evaporator or the product being further enriched in unsaponifiable valuable substances obtained from the third high vacuum evaporator can be further purified, for example, by crystallization means, to obtain sterols.
The sterols can be crystallized by any known method involving a solvent mixture comprising at least one, preferably at least two, of the solvents selected from the group consisting of ketones, alkanols, hydrocarbons and water. A preferred solvent mixture comprises methyl ethyl ketone, methanol and water. Another preferred solvent mixture comprises a hydrocarbon, methanol and water.
Other solvents/solvent combinations can be used to crystallize the neutral substances as well. It is known to one of ordinary skill that pure pine based raw material, mixtures of hydrocarbon, methanol and water are suitable. These solvents/solvent combinations include other lower alcohols, their mixtures with themselves and, for example, mixtures with hydrocarbons and/or ketones and/or water.
According to the invention, the crude sulphate soap, the saponified crude tall oil, or the saponified tall oil pitch can be in the form of sodium soaps or potassium soaps or even mixtures thereof. Such sodium and/or potassium soaps can be produced by saponifying crude tall oil or tall oil pitch with a sodium or potassium soap-forming compound such as sodium hydroxide or potassium hydroxide.
The soaps can also be xe2x80x9cmetalxe2x80x9d soaps, such as zinc, iron, manganese, magnesium, calcium or aluminium soaps. Such soaps can be produced by reacting a sodium or potassium soap with a metal soap-forming compound. The crude tall oil or tall oil pitch can also be saponified with a metal soap-forming compound to produce the corresponding metal soap. By using metal soaps, the amount of the softener can be reduced. Furthermore, blends of such metal soaps and sodium/potassium soaps can be used.
According to the invention, the evaporation residue from the first high vacuum evaporation can be further processed, for example by acidulation, to obtain acids, such as fatty and rosin acids. The residue from evaporation contains the softener used in the prior step and this softener can be recovered and be used. By using vegetable oils (such as triglycerides) as softeners, these softeners can also be hydrolysed to obtain fatty acids.
Unsaponifiable valuable substances other than sterols can also be obtained by the process according to the invention. For example, wax alcohols can be obtained as the distillate after performing the second high vacuum evaporation.
The following examples describe the invention more closely. In this specification, the symbol xe2x80x9c%xe2x80x9d refers to percentages by weight unless otherwise specified.